List Segmentation: I would have to say the number one feature is the ability to tag and segment subscribers based on their behavior. This allows you to follow up with leads based on the specific actions they take (or don’t take). For example can tag links inside emails so when your subscriber click on it you will know. You will have the power to create list segments based on any field in your database.

When your list goes above 2000, and you decide to move to another AR service, you will get an unpleasant surprise. Mailing lists are not directly transferable from one AR service to another. You basically have to start over, and get all of your subscribers to re-subscribe. That process will guarantee the loss of at least half of your list, and probably much more than half. If you are thinking about moving, the time is NOW, because the larger your list gets, the more painful the move will be.
AWeber helps organizations turn passive prospects into loyal customers with email marketing and automation tools with live customer support. Choose from hundreds of ready-to-use sign up form templates and add custom branding – without coding skills. Watch people subscribe via the website, blog posts, Facebook page, in-person events and anywhere else audiences hangs out.
Receive periodic updates about new subscribers to your email list, without cluttering your email inbox with individual notifications for each new subscriber. Use this Zap to automatically add new AWeber subscribers to Zapier's Digest tool. Zapier will then deliver the digest to you via email on a daily, weekly, or monthly basis. That way, you'll have an organized round-up delivered to your inbox with your new AWeber subscriber information.
Don't waste time copying contact information between your different platforms. Zapier automation can handle tasks like that for you, saving you time for more important work. This integration will trigger with every new user added on Teachable, and pass their details over to Aweber as a new subscriber so you can keep them updated on all your offerings

Synchronises customer data of your newsletter subscribers to the AWeber list you select. * Stores relevant customer data in your AWeber subscriber list. Not only the name and email of your customers are stored in your AWeber account, but also their address data and customer information like the amount of orders in your webshop and the total amount they spent. This greatly increases your segmentation options. * Synchronises your customer data to your AWeber list every 15 minutes. This means your AWeber subscriber list remains up-to-date and you can optimize your autoresponder strategy by sending new customers emails within a few days. * Note that opt in emails are sent to your customers by default. If you don't want this to happen, you can disable them in the List Options page on the tab 'Confirmed Opt-In'. You can switch off option 'Send a confirmed opt-in email for Imports'.